1. Field of the Invention
Embodiments of the present invention generally relate to increasing the data bit density in a hard disk drive. Specifically, the invention relates to modulating and synchronizing a radiation source to aid in writing data to high coercivity media.
2. Description of the Related Art
Perpendicular magnetic recording, where the recorded bits are stored in a planar recording layer in a generally perpendicular or out-of-plane orientation (rather than parallel to the surface of the recording layer), is a one path toward ultra-high recording densities in hard disk drives. The perpendicular magnetic recording layer is typically a continuous layer on the disk substrate, like in conventional magnetic recording disk drives. The media comprises a plurality of magnetic elements called grains. As the areal data density (the number of bits that can be recorded on a unit surface area of the disk) increases, the magnetic grains that make up the data bits can be so small that they can be demagnetized simply from thermal instability or agitation within the magnetized bit (the so-called “superparamagnetic” effect). Accordingly, the magnetic material (or media) of the grains is chosen to have a sufficiently high coercivity such that the magnetized data bits are correctly written and retain their magnetization state until written over by new data bits.
Generally, optical energy may be focused onto a spot of the magnetic material to heat the spot and lower the coercivity of the magnetic material. A write head projects the desired magnetic field through the heated spot which aligns with the grains of the heated spot to the magnetic field. As the spot cools, the coercivity increases and stabilizes the magnetic field of the high-anisotropy layer. Thus, a read sensor is able to pass over the spot, detect the magnetic field, and interpret the bit pattern. This technique is broadly referred to as “thermally assisted (magnetic) recording” (TAR or TAMR), “energy assisted magnetic recording” (EAMR), or “heat-assisted magnetic recording” (HAMR) which are used interchangeably herein.